Monday, 28 December 2020

Herald of a Revolution

The decision to mass produce the T-44 medium tank was made in the summer of 1944. This happened not only before the final prototype indexed T-44A was built, but before the GBTU even composed tactical-technical requirements for a new tank based on the combat experience of the first half of 1944. As a result, the tank seemed obsolete before it was even put into production, especially its armament. Work to correct this went in two directions. The first was evolutionary and led to the T-44-100 tank. The second was revolutionary and brought about a deeply modernized T-44 indexed T-54.

Chasing after requirements

The GBTU's requirements for armament and protection of tanks grew constantly during the first half of 1944. This was in part due to the use of new tanks in battle in the spring of 1944. The NIBT proving grounds had its own ideas about these requirements and also sent staff to the front lines multiple times. They composed tactical-technical characteristics that eclipsed even those set by the GBTU. The tank would weigh up to 35 tons and have a top speed of 45-50 kph. The front hull armour would be 90-100 mm thick and the turret front would be 120-130 mm thick. This requirement came up after study of the IS-1 tank. The desired turret ring diameter increased to 1700 mm and an electric turret traverse motor like on the American Medium Tank M4A4 was requested.

A 76 or 85 mm gun with a muzzle velocity of 1000 m/s would be the main armament. There would be two machine guns: one coaxial and one in the rear. 6 smoke grenade launchers would also be mounted on the turret. This solution was copied from the Germans. The suspension still used torsion bars, but shock absorbers were added in the front and rear.

The first installation of a 100 mm gun into the T-44A, summer of 1944. This tank is based on the draft project, the one built in metal looked different.

These requirements were still rather conceptual, but they were developed into new requirements from the GBTU. These requirements were even more vague. The crew of this new tank would consist of 5 men, the thickness of the armour was not specified. The gunner and loader would trade places in order to make the work of the latte easier, this solution was used in tanks with S-34 guns developed by the TsAKB. These flights of fancy led to a turbulent dialogue between the GBTU and NKTP. The NKTP calculated that the tank the GBTU wished for would need 100 mm thick front armour, 170 mm thick turret armour, 120-160 mm thick hull sides, and 125-160 mm turret sides. 

Just the empty hull and turret would weigh 30 tons, and the full tank would weigh about 55 tons. The NKTP also rejected the GBTU's idea of installing two belt fed machine guns on the fenders. The NKTP proposed installing a bow machine gun instead, but the GBTU insisted. The requirement for a 620 hp engine was shocking, as no such engine was in production and did not appear even in the late 1940s. The requirement for a night vision device was also a surprise. Soviet tanks first used night vision devices in the fall of 1942. Their design needed improvement, but by 1944 there was little progress. Improved PTsT-8 night vision devices were under test since 1943, but the results were not encouraging. The NKTP hinted that the GBTU's requirements were not aligned with reality.

Sectional view. The tank's name is shown in the lower right corner: T-44A. Some sources named this tank T-44V, but there was no such tank even on paper.

Meanwhile, factory #183's KB-520 continued independently working on an improved T-44. The fact that this work was being performed on the factory's own initiative is confirmed by its absence in the list of experimental work signed by Malyshev on August 22nd, 1944. Interestingly enough, this project had the same index at first: T-44A. Some researchers named this project T-44V, but that was caused by a misprint (a Cyrillic В instead of a Б). The gun mount was developed using the documentation from the T-44A. Surviving drawings show the variable thickness hull sides and the old style of hull and turret with a cast front and rolled sides and rear.

The project's name was changed to T-44B in the fall of 1944. Its design also changed. The idea of using a composite turret with rolled sides and rear was discarded due to complexity. As experience with the T-34-85M showed, armour components with variable thickness could be cast. A new cast turret with a welded on rolled roof was designed. Factory #183 clearly received the GBTU's requirements, and so protection increased. The front of the turret was up to 150 mm thick and gradually thinned out to 90 mm. The turret ring was widened to 1800 mm to help with fitting the 100 mm gun. As for the hull, the configuration was the same as the T-44, but the thickness of the front armour increased to 120 mm and the sides to 90 mm. The driver's vision slit was removed to improve protection and replaced with periscopes.

A tire from the widened T-44A road wheel. It was first installed on the T-54 prototype.

There are no precise dates for development of the T-44B known, but factory #183's report on experimental work for October states that all hull components were complete by the end of the month. Morozov travelled to Moscow with materials related to the project where it was approved by Fedorenko. Malyshev also gave his approval. Order #637s was signed on November 1st, 1944. It compelled factory #183 to provide detailed blueprints by December 1st. An "IS-6 style turret" without a commander's cupola was required. The maximum weight was set at 34 tons. The road wheels would be widened. The tank also received a new index: T-54. However, the index T-44B remained in use in November and even throughout December.

Growing armour and armament

Order #637s retroactively authorized work that began in October of 1944 at factory #183. In addition to starting work on the hull, KB-520 began working on a coaxial mount for the D-10T cannon and SG-43 machine gun. The hull was assembled in November and the main mechanisms were also completed.

The first T-54 prototype at the NIBT proving grounds in February 1945.

As required in order #637s, KB-520 developed a turret similar to the one designed for the IS-6. This type of turret design was considered optimal, but the GBTU and NKTP were in for a shock. Trials of two IS-6 turrets cast from 70L and 72L steel were conducted in January of 1945. Trials showed that the 150 mm thick side was penetrated by the 88 mm Pak 43 L/71 after a second shot. Another pair of hits resulted in penetration of a section with 160 mm of armour. Finally, the rear could be penetrated by the 75 mm KwK 42 L/70. After the fifth shot the 72L armour cracked. The turret made from 70L steel was more satisfactory, but it was clear the the NKTP and GBTU were mistaken about the shape. However, this all happened later. As of late 1944, the IS-6 shape was considered the priority.

A device to the driver's left improved visibility.

Even though the factory reported completion in November of 1944, the turret was actually finished in January. Factory #183 interpreted the requirement to make an IS-6 style turret very creatively. The turret was similar to the T-44 design, but improved. There was a certain influence from the Object 250, but the design was quite original. It was low, lower than even the T-44's already low turret. The armour was improved compared to its predecessor. The front was 180 mm thick, the mantlet was 150 mm thick, the sides had variable thickness from 150 to 90 mm, and the rear was the same as the T-44: 75 mm. Due to a more powerful gun the turret ring was widened to 180 mm. The roof was made from three plates. The MV-12 motor driving the ventilation fan was kept as is, but the fan dome was enlarged. As requested, the commander received a lowered cupola with a periscope in the rotating portion. 

Protection from the front radically improved due to a revision of the driver's observation devices.

The armament consisted of a 100 mm D-10T gun and a coaxial SG-43 machine gun. The T-54 was the first tank to use this machine gun. Like the T-44, the turret received a MB-20V electric traverse motor and an MV-26 motor for elevating the gun. An indicator for when the gun traversed past the sides of the hull was also added. The turret developed for the T-54 tank also inspired the turret made for the T-34-100. It had a slightly different layout and also much thinner armour.

The chassis was mostly the same a the T-44's, but with some changes.

Work on the running gear, primarily the road wheels, went on in parallel with the turret. Issues with road wheel tire lifespans continued to be a problem in 1944 and 1945. Trials of road wheels with internal shock absorption took place in late 1944, but the results were negative. The second solution was the development of a wider T-44A road wheel. The diameter remained the same at 830 mm, but the width increased to 185 mm. The wheel was developed in September of 1944, but not produced for a very long time, as factory #183 had no rubber coating facilities. Finally in January of 1945 factory #563 produced a test batch of wheels for the T-54 prototype. Factory #75 that was waiting for two sets of wheels did not receive any. The widened road wheels could not be used on the T-34-85, as it fouled the suspension arm. The suspension arms on the new tank had to be changed to accommodate them. They were now cast in one piece, unlike before.

Naval smoke bombs were carried on the rear.

The January report estimated that work will be complete on February 15th. The prediction was spot on: assembly was finished on February 14th. Gunnery trials followed. Trials showed that the gun didn't always return to battery and extraction sometimes failed. Nevertheless, factory #183 considered this acceptable for brief trials. The tank drove for 50 km to the shooting range and back, showing no defects. On February 16th, 1945, the T-54 and T-34-100 were sent to the NIBT proving grounds.

Thanks to the lower turret, the T-54 was lower than its predecessor, even if it was much heavier.

The designers didn't meet Malyshev's requirements for mass. Instead of 34 tons, the T-54 weighed 35,850 kg. This was linked to a significant increase in protection. Like on the initial T-44B project, the front of the hull remained at 120 mm, the sides were thickened to 90 mm. The layout was the same as on the T-44, but the hull was now 54 mm longer. The distance between the first pairs of road wheels increased as a result. The turret platform was also changed due to the larger turret ring. The sides didn't need KV-85 style addons, but there were additional patches welded on in that area.

T-54 armour diagram.

In addition to thicker armour, the prototype also had a reworked driver's station. The driver's observation slit was removed from the front plate, which improved its robustness. A retractable periscope was added on the hull roof instead. The periscope had a cover on top. Another periscope was added on the left side. The MK-IV periscope on the driver's hatch also remained in place. This solution improved observation.

Like the turret machine gun, the bow machine gun was also replaced with a belt fed SG-43. The ammunition racks changed to accommodate the new ammunition types. 34 rounds were carried for the D-10TK gun: 20 in the front rack, 5 on the floor of the fighting compartment, 6 in the turret bustle, 3 on the right side of the turret. The ammunition capacity decreased compared to the T-44, but the roomier SU-100 carried even less ammo: 33 shots. The ammunition racks for the machine gun also changed. Unlike the cannon, there was now much more ammunition for the machine guns: 3000 rounds.

Location of the ammunition. The amount of ammunition carried was much less than on the T-44.

The engine was the same as on the T-44. However, KB-520 improved a number of systems. A space heater was added to the cooling system and the radiator was now composed of four sections. A heater was also added to the air cleaner, which made the tank easier to start in the winter. The fuel system changed little, but the overall fuel capacity increased to 530 L. Changes were made to the final drives, as well as the road wheels and suspension arms.

The commander's cupola was lowered as required, which resulted in poorer visibility for the commander.

The lower turret meant that the T-54's height decreased to 2275 mm. Factory documentation contained an error and stated that the height was the same as the T-44: 2400 mm. The fighting compartment height was 1570 mm, 20 mm lower than on the T-44. Since there were nearly no mobility trials performed at the factory, the mobility characteristics were all calculated. The top speed was estimated at 53.5 kph, which turned out to be overly optimistic.

Room for improvement

The tank's road to the NIBT proving grounds was a long one. It only arrived in Kubinka on March 10th and managed to go on a drive in the meantime. The odometer read 227 km (other sources say 193 km) on arrival. Joint NKTP and army order #92s/021 was signed on February 28th, while the tank was en route. It stated that trials must start on March 1st and complete by March 21st. A report was expected on March 25th. These tight timelines were explained by the fact that the T-54 looked a lot more promising than the T-44, and the question of putting it into production was an urgent one.

Trials were late to start for various reasons.

In practice, the trials started only on March 11th. The vehicle was studied and prepared for trials. The driving trials would cover a standard distance of 1000 km: 400 on a highway, 530 on dirt roads, 70 km off-road. As it usually happens, the real distance was somewhat different. The tank began mobility trials on March 13th and finished them on April 9th. The full trials finished on April 14th, almost a month after the deadline in the order.

Trials on slopes showed that the traction in snow was insufficient.

The tank drove for 1553 km in total: 450 on a snow covered dirt road, 475 on a muddy dirt road, 416 on a paved highway, 141 off-road, and 71 during gunnery trials. The highway was covered with 5-8 cm of packed snow, only the last 100 km were directly on pavement. The results were far from calculated. The top speed was 43.5 kph, 10 kph lower than calculated. Normal speed varied from 23.1 to 42.1 kph when driving on pavement. The average speed was recorded as 34 kph, but this was lowered as the tank was constantly stopped to measure the temperature of the road wheel tires. Nevertheless, it was clear that the top speed was overestimated. Even 50 kph was too much not just for this tank, but for later prototypes. This was the cost of improved armour. Fuel expenditure was 153 L per 100 km, giving a range of 320 km before refuelling.

Even though the tank was heavier than the T-34-85, its mobility in winter was similar.

As with the T-44 prototypes, driving off the highway was done in near extreme conditions. The dirt road was either covered with deep snow (40-60 cm) reduced to mud. The tank's average speed in these conditions was 15.2 kph. The T-34-85 reached a speed of 17.7 kph in these conditions. The fuel expenditure was also higher. The tank burned 305 L of fuel per 100 km of driving in snow and 268 L per 100 km when driving in mud. In these conditions the driver had to periodically wipe off his observation devices. This was not hard, all he had to do was crack open the hatch and wipe off his periscope. This could be done without stopping.

Driving on a tilt.

Special trials showed that the tank couldn't climb a slope steeper than 13-15 degrees due to insufficient traction. The aforementioned T-34-85 with the same tracks didn't show any better results. After spurs were installed, the tank could climb a 25 degree slope. The greatest tilt at which the T-54 could drive was 15-16 degrees. Considering the difficult conditions, these results were acceptable. The tank also knocked down a 530 mm thick pine tree during felling trials. The T-54 was not hard to drive. Steering levers took 14-15 kg of effort to operate when turning and 18-20 kg when rotating in place.

The T-54 at tree felling trials.

One of the most important observations was that there was no need to replace any road wheels. Issues were only observed with the third right wheel. The defects discovered did not stop the tank from completing the trials. Even after the trials were completed the damaged road wheel was deemed fit for service. Of course, the prototype had plenty of issues (bent and broken suspension arms, broken travel stops) but the main problem Soviet medium tanks suffered from was solved. 

A 530 mm thick pine tree was knocked down on the first attempt. Bigger trees took several tries.

The results of gunnery trials were also interesting. As mentioned before, the tank was built with a 100 mm D-10T gun, but it was never fired. On March 23rd-24th it was replaced with a new gun, a D-10TK. It had several differences from the D-10T. The spring balancing mechanism was removed, the design of the tube and guard rail changed, an electric firing mechanism was added, as well as a spring compensator. This system was put through trials. Precision was within acceptable norms and aimed rate of fire was recoded at 4.5-5.4 RPM depending on the ammunition rack used.

The aiming mechanisms were also tested. The electric traverse motor could rotate the turret completely in 10 seconds (compared to 2 minutes 30 seconds by hand). Elevation was harder. The full 26 degree range could be covered by the gunner in 50 seconds if he used both hands. The electric drive helped, but not much: 20 degrees in 15 seconds. The difficulty in gun elevation affected the precision of fire on the move. It was judged to be unsatisfactory. The traverse mechanism was also criticized. There was a backlash and the electric motor could not aim the gun precisely. The concentration of fumes in the turret was also too high. The NIBT proving grounds staff suggested improving the fan and also add a bore evacuator.

Testing the smoke bombs.

The crew workspaces also drew criticism. The requirement to make the commander's station like the one on the IS-6 led to reduced visibility. There were also complaints about the sealing of the commander's hatch. His seat was not adjustable vertically and there were also other complaints. The turret traverse button was deemed a good idea, but it needed improvement. The gunner's station was also not ideal. The traverse mechanism was not ideal and there were other drawbacks. The seat was uncomfortable, the TSh-19 sight was too close to the recoil guard, the electric trigger was badly positioned and got in the way of the loader. The loader's station also had its drawbacks. When he was using his MK-IV periscope there was an ammo crate right by his temple. A lack of a turntable was listed among the overall drawbacks of the turret design. The driver's station was no worse than on the T-44, but there were still complaints. The seat had to be made more robust and the lever and pedal positions had to be changed like on the production T-44. A removable windshield was also requested. Visibility was generally judged to be poorer than on the T-44. This was an unpleasant conclusion, as before this each new tank from KB-520 had better visibility.

Visibility from the T-54 tank was worse than the T-44.

The hull and turret design were also criticized. Attaching small parts to the front of the hull, especially the idler carriers, was deemed a bad idea. The joint between the hull front and sides was deemed insufficiently robust. As further trials of the T-44 proved, this was a correct call. The joints between the sides and floor was also bad, as theoretically it could be penetrated even with an anti-tank rifle. There were also complaints about the engine deck grilles. Finally, the turret was deemed a poor design and not as resistant to fire as the front hull. This applied both to the turret overall and the gun mantlet. The NIBT proving grounds proposed a new design for the turret based on the IS-3.

The road wheel tire after 1500 km of driving. Despite a number of defects, it was deemed suitable for further service.

The final verdict was mixed. On one hand, the tank surpassed the T-44 in armament and protection and also passed mobility trials. On the other hand, there were many drawbacks. The tank was good, but there were issues to be corrected before it could be accepted into service. The T-54 was recommended for service, but not in the form in which it was delivered for trials.

A time of waiting

Such a large list of changes meant that the tank needed a lot of work. Nevertheless, the NKTP and GBTU were still very much interested in it. The tank arrived at the Gorohovets artillery proving grounds on May 3rd, 1945, where it took part in gunnery trials from May 10th to May 12th. The report calls the gun D-10T, although it is clear in photographs that it's a D-10TK. The proving grounds trials showed that the precision was worse than expected, but the rate of fire was higher: 6.3 RPM. The tank's entire ammunition supply was fired in 10 minutes 30 seconds. The crew reported feeling well, although the loader was lightheaded. The gun fired 250 shots without issue, but there were still the same complaints about the commander's station and the aiming mechanisms. The tank definitely needed more work.

The tank on trials at the Gorohovets proving grounds. The distinctive D-10TK barrel can be seen.

These conclusions didn't get in the way of Malyshev signing NKTP order #217ss on May 5th, 1945. This order instructed factory #183 to send T-54 blueprints to factories ##75, 264, 112, 174, and the Mariupol factory. This was necessary to prepare for mass production of the new tank. Meanwhile, factory #183 didn't sit idle. By May of 1945 KB-520 developed a new planetary turning mechanism, planetary gearbox, and five-stage synchronized gearbox. The NKTP responded with order #246s dated May 19th, 1945, calling to install and test these components. In June they were joined by a new air cleaner developed at factory #100. An analogous design was required from KB-520 for the T-54.

Despite what some sources say, the second T-54 prototype looked nearly identical to the first one.

A second T-54 prototype was built in June of 1945 as a result of the trials. Some authors claim that this tank had a number of differences: a new turret, altered hull, LB-1 cannon, two machine guns on the fenders instead of one in the hull, etc. In reality this was not the case. According to a report from factory #183, the tank was assembled from existing stock of parts. Not a single request from the NIBT proving grounds was taken into account, and so the tank was externally identical to the first prototype. Only the armament and some elements of the transmission changed. First of all, the tank had the new KS-D-10 gun. Factory trials showed that it worked well. Second, the tank had a new synchronized 5-speed gearbox as well as planetary turning mechanisms. Issues with the turning mechanism were discovered during the 300 km run, which meant that it needed more work. As for the other development, it was paused for an unexpected reason:
"The entire design bureau except for two teams (turrets and observation devices) are busy with the 10 ton Mack truck: making drafts and blueprints, establishing tolerances, etc."

Mack NR heavy truck. This was a significant obstacle to T-54 development in the summer and fall of 1945.

Factory director Maksarev gave the order to study and develop documentation for the heavy American Mack NR truck on July 12th, 1945. This was not his own initiative, but an order from Malyshev. Such a strange turn of events for the KB-520 design bureau had an impact on the T-54. Work on the tank stalled. New pin gear drive sprockets and tracks were only developed by October of 1945. The new turret (the aforementioned IS-3 type) designed for the LB-1 100 mm gun was still in its early stages. As for the second prototype, it had driven for 1200 km by October 10th. Many running gear and transmission defects were noted. It drove for another 200 km in October. Military QA demanded that the government intervene, since KB-520 was busy with its truck instead of working on the T-54 or anything else. The situation changed only towards the end of 1945. Despite all issues, the improved T-54 was taking shape. This tank differed significantly from the T-44 and T-54 prototypes, but that's a whole different story.

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